Running-in of aluminum/steel contacts under starved lubrication: Part I: surface modifications

In Part I of this two part paper, extensive surface analysis is done to examine surface changes caused by different run-in procedures on 390-T6 aluminum pins sliding against 1018 carburized steel disks. The area contact is lubricated by a base polyalkylene glycol (PAG) lubricant mist carried by a tetrafluoroethane (R134a) refrigerant gas under starved lubrication conditions. Surface traces and elemental analysis through Auger Spectroscopy and X-ray diffraction are conducted on virgin and run-in specimens to determine whether surface smoothing or film formation dominates the running-in process. Run-in pressure, velocity and time as well as the effect of the friction coefficient during run-in are examined. Limited data are also obtained for different degrees of starvation. The results show that surface smoothing increases with run-in pressure and occurs within the first minutes of sliding. Longer run-in times allow for the formation of iron oxides as well as Al–Fe intermetallic compounds on the aluminum pins. The iron transfer to the pin is due to the abrasive action of the silicon particles on the steel disk.